Non-Geostationary satellites (“NGS”) for applications of broadband multimedia satellite communications (“BMSC”) are being addressed more often in recent years. Due to the nature of NGS that is not stationary with respect to the earth, many satellites in orbits are always required to provide continuous services for global coverage. Hence, the satellite constellation design is one of critical technology to insure the success of BMSC via NGS (“BMSC-NGS”). Highly elliptical orbit, such as Molniya proposed by Russian, is good for a relative smaller region of coverage. Moderate elliptical orbit is more suitable to half hemispherical coverage. Near circular orbit is ideal for global scale coverage such as Iridium, Globalstar, Odyssey, Skybridge, Teledesic, etc.
The polar orbit satellite constellation of Iridium system of Motorola is based on the design concept presented by W. S. Adams and L. Rider that all of six orbital planes are inclined at the same inclination angle of 86.4 degrees. Each orbital plane consists of eleven satellites. Polar orbit constellation has a great concentration of satellites near the poles of earth where there are not many people lived there. The Globalstar system of Loral, satellite programs of the Skybridge of Alcatel and Odyssey of TRW used inclined orbit satellite constellations that had been studied extensively by J. G. Walker. The orbital planes of satellite constellation design in these systems are all inclined at the same prograde orbits (inclination angle between 0 and 90 degrees) with the inclination angle closed to 52 degrees. The constellation design of these three systems tends to provide more uniform distribution globally than of the polar orbit. The orbital planes of satellite constellation design in the Teledesic system are all inclined at the same retrograde orbits (inclination angle greater than 90 degrees) with the inclination angle closed to 98.2 degree.
It is noted from previous arts and earlier constellations designs that there are common deficiencies and issues did not addressed. None of the previous arts have addressed the important topic that how to simplify satellite tracking problems of the user's antenna via satellite constellation design. In order to achieve continuous services of a quality communication, the user's antenna must be able to track each NGS being linked and the next coming NGS to be connected simultaneously during the transition period of these two satellites discussed above. The satellite communication system s based on previous arts of the constellation design will require two separate antennas or two separate antenna beams so that they are able to track these two satellites, being linked and to be linked next, correspondingly and simultaneously over a very wide field of view across the sky. Hence, it is difficult to realize low cost user's antenna systems for BMSC-NGS applications based on previous arts of satellite constellation design.
The other important topics did not address from the previous arts of the satellite constellation design are that how to eliminate the potential interference issues with GEO satellite and terrestrial communication for the applications of BMSC-NGS. The minimum elevation angle of a user's antenna pointing toward the satellite is typical at 10 degrees or less for the NGS system based on previous arts. As user's antenna pointing at low elevation angle, the potential interference with terrestrial communication and the blockage problems from the surrounding structures of user's antenna are becoming serious issues for the BMSC-NGS applications. The potential interference with GEO satellites will also limit the BMSC-NGS applications for users near the equatorial regions (e.g. between latitude 10S and 10N degrees).
The effective way to eliminate the interference with the GEO satellites is to point user's antenna away from the GEO satellites. User's antenna always pointing at high elevation angle is the only way to eliminate the potential interference issue with terrestrial communications and minimize the blockage problems from the surrounding structures of user's antenna. The best way to achieve a simple tracking of the NGS of user's antenna is to enable user's antenna to track satellites in continuous link loops.
The objective of the present invention is to solve these deficiencies of previous arts mentioned above so that NGS could be used widely for broadband multimedia communications in the future. The constellation design based on the present invention will simplify the satellite tracking problems of user's antenna and completely eliminate the interference problems with GEO satellites and terrestrial communication services. The blockages from the surrounding structures of user's antenna will also be minimized because user's antenna is able to point at high elevation angle for the satellite constellation system based on the present invention.